Review Flashcards
define systems neuroscience
the science of the structure and function of neurons and neural circuits that compute adaptive behavior
define behavior
internally coordinated response to internal/external stimuli. must be theologically adaptive to be considered relevant behavior
Marr’s 3 levels
1) computation; why (problem) [flight]
2) algorithm; what (rules) [flapping]
3) implementation; how (physical) [feathers]
Functional-anatomical localization across scales
early subdivisions came from cytoarchitecture
now, we have techniques like patchSeq (mix of ephys + transcriptome), includes morphology
observed in topographical maps (visual columns, homonculi in motor/sensory)
including different lobes of brain!
Hierarchical organization of circuits and systems
think about visual system. there’s the dorsal and ventral streams, and recurrent connections throughout.
also includes mixed selectivity of PFC
cautionary note, lots of recurrent connections! also v1 neurons are tuned differently during motion than when static
feedfoward, convergent integration allows for output neuron to do what?
be selective, it can recognize features that any of the 1 input neurons can’t! Think V1 simple cell RF, center on, surround off
What are some computations that lateral inhibition is used for?
selectiviy in MT cells in OB. also, stable, winner-take-all ring attractor network in hippocampus
define selectivity
refers to ability of neurons to selectively respond to specific features or properties of a stimulus
define gain modulation
refers to a change in the overall sensitivity or responsiveness of a neuron to input without necessarily changing its selectivity.
phenomenon whereby the gain or sensitivity of a neuron to inputs is altered w/out changing selectivity
Transfer Function
Input/Output relationship: relationship between inputs a neuron receives and the firing rate responses of that neuron
Potential Neural codes
rate code
population code
latent population dynamics
latency-based code
what is a memory sytem?
learning is the process of acquiring new information while memory refers to the persistence of learning in a state that can be revealed at a later time
Karl Lashley
rats in mazes. lesioned cortex and examined performance. concluded that extent, not location of lesion determined behavioral impairment
Wilder Penfield
Mapped brain while performing surgery on patients w/ epilepsy
Stimulating temporal lobes could prompt memory recall
Brenda Milner
HM
Following surgery, he had anterograde amnesia. remembered some memories from childhood, but lost many more recent memories.
was able to learn some new tasks
Multiple Memory Systems
into what 3 stages can memory be divided?
acquisition (encode), consolidation (store), retrieval (retrieve)
consolidation can be cellular or systemic consolidation
Dentate Gyrus circuit organization
FF excitation w/ divergent connectivity. EC to DG (1:5) expansion from entiorhinal cortex to dentate gyrus
key circuit organization features of dentage gyrus
expansion/divergence of inputs
feedback and lateral inhibition
sparse connectivity between inputs to dentate granule cells
– leads to pattern separation . evidenced by square/circle morph
increase memory capacity/specificity
Hippocampus CA3 circuit for rapid encoding and pattern completion
CA3 receives input from EC, DG and recurrent autostim from itself!
auto associate network for rapid encoding and pattern completion.
results in auto-associative fixed-point attractor network (falls into one of 2 valleys)
how does spatial peridocity of grid cells change in MEC?
along DV axis! more close together in Dorsal
what circuit motif allows grid cells?
structured lateral inhibition
how do we get from grid cells of MEC to hippocampal place cells?
feedforward linear integration model!
D1 Action Selection
D2 pathway for action selection
Dorsal Ganglia Chuck Image
Action Selection: Movement
selects particular movement
triggers initiation and termination
scales amplitude, speed and force
Action Selection: Motivation
Drives ideation/cognitive focus
modulates emotional response
sows impulses, obsessions, compulsions and addictions
Procedural Learning
motor chunking
- complex skill acquisition
habitual behaviors
-stimulus-response associations
goal-directed behaviors:
-action-outcome associations
what is most responsible for reinforcement learning?
phasic dopamine!
Implicit Memory Summary
dopamine sourced from SNc and VTA
-targets essentially all action selection loops
tonic dopamine maintains baseline activity level
phasic dopamine associated w/ unexpected reward
-strengthens synaptic pathways of selected action
sensorimotor learning:
DLS, stimulus response reinforcement drives habituation, egocentric
assocative learning
DMS, action-outcome reinforcement drives cognitive learning and more strategic problem-solving approaches
reversal learning
DMS A-O necessary to unlearn DLS S-R
Delay timing paradigm
Trace timing paradigm
simultaneous timing paradigm
backward timing paradigm
things to note about fear learning and acquisition curve
learning occurs at different timescales.
asymptote is controlled by strength/intensity of US (gamma)
rate of acquisition is controlled by CS saliency (alpha)
Delta_V = alpha(gamma-epislon*V)
Mouriel Consolidation
fear circuit
Half Center Model
Lamprey CPG
pyloric circuit
driven by intrinsic oscillation
What are differences between data collected in extracellular recordings vs intracellular recordings?
Patch-clamp: monitors current or voltage from inside cell. also able to manipulate neural activity.
extracellular recordings monitor voltage only from outside of the cell
Principles of Spike Sorting
1) Filter to separate spikes from LFP
2) identify all spikes
3) use clustering methods to classify individual spikes as comprising “single units”
4) reconstruct spike train from each single unit.
Limitations of electrodes
physically invasive
low spatial resolution
limited throughput
specificity is conferred by position, not cell type or molecular features
problems w/ small-molecule dyes
injections are invasive
dyes are often toxic
imprecise
how can you find behaviorally relevant neurons from calcium signal?
regression analysis! can use knowledge of stimulus and animal’s behavior to predict what a behavior-encoding neuron would look like! This is done by convolving the impulse response w/ other known factors like stim. intensity or tail angle
how does channelrhodopsin work?
it works as both an opsin and an ion channel! when stimulated with light, the channel opens and drives membrane potential
what’s different about halorhodopsins?
they inhibit cells by allowing Cl- into the cell
What are DREADDS
designer receptors exclusively activated by designer drugs
examples of some good manipulations of sensory environment?
postnatal exposure to a vertical world prvents devleopment of the ability to see horizontal features.
monocular deprivation prevents development of the ability to see in deprived eye
glasses on young owls that shift the world 10 degrees when trying to use sound to locate something
how are odors encoded?
in a combinatorial, across-fiber code
how are gloms tuned at low odorant concentrations?
narrowly tuned and extremely sensitive
although odor may be encoded by population
how are gloms tuned in chemical space?
coarse, spatial map of glomeruli w/ similar tuning in chemical space and distinct domains for class I and class II receptors
how does OB circuit shape glom representation of odor?
dendrodendritic inhibition
circuit motif in OB for gain contorl
intraglom feedforward and presynaptic inhibition. may also filter weak inputs
what circuit motif sharpens OB receptive field?
lateral (interglom) inhibition
how does odor mapping change from OE, to OB to PC
Piriform representations of odors?
not odotopic, combinatorial
Taste transduction
1) pass directly through ion channel (salty/sour)
2) bind to GPCR which activate 2nd messengers (Umami, sweet, bitter)
taste coding in periphery
labeled lines
after most peripheral taste neurons, how is taste encoded?
mix of labeled lines and across-fiber pattern
gustatory cortex neurons are tuned to both taste as well as other taste-adjacent behaviors
what makes dynamics of taste encoding unique?
taste responses are dynmamic and different aspects of a taste stimulus are encoded at different times
taste specific neural states occur across the gustatory cortex population
define flexor and extensor
flexor: reduce joint angle when contracted
extensors: increase joint angle when contracted
minimal controls for locomotion
start signal
flexor extensor pair on same side must alternate
contralateral limb cycles must be anticorrelated
fore/hind limb cycles must be anticorrelated
potential sources of oscillation
Cell-intrinsic: The cell’s complement of ion channels and membrane properties generates cycles of activity and inactivity spontaneously, without external inputs.
Network-mediated: Reciprocal inhibition between pairs of neurons, combined with synaptic fatigue, post-inhibitory rebound, equires synaptic fatigue, post-inhibitory
rebound, or adaptation to a tonic excitatory input
what are important about Shox2+ interneurons?
Shox2+ neurons generate the motor rhythm in mammals.
Evidence: (1) They fire rhythmically during locomotion;
(2) Blocking glutamate release from Shox2+ neurons disrupts the rhythm;
(3) They are excitatory and ipsilaterally- projecting (analogous to lamprey equivalents)
how could one broadly distributed excitatory input to sC could be used to control locomotor speed?
Firing rates in nMLF neurons are directly correlated with swim speed, and the spinal motoneurons/interneurons that fire during fast swimming have a lower input resistance than those that are recruited at slower swim speeds. If nMLF neurons provide equivalent excitatory drive (synaptic strength) to all spinal interneurons and motoneurons, then as nMLF firing rates increase, additional ‘fast’ spinal neurons will be recruited, and swim speed will increase.
Identify two behavioral functions that cannot be adequately mediated by subcortical motor
pathways.
“Dexterous” movements of the extremities.
Motor learning/skill acquisition.
what drives leech cardiac CPG?
reciprocal inhibition
what kind of neurons generate motor CPGs?
ipsilateral glutamatergic interneurons provide rhythmic excitation to primary motoneurons and to contralateral projecting inhibitory neurons
inhibitory neurons coordinate L/R alternation
candidate motor CPGs should fill which criteria?
excitatory and project ipsilaterally to motor neurons and contralateral to inhibitory interneurons
what does reticulospinal tract control?
axial movements, balance, limb movements, modulates corticospinal signals, locomotion
what criteria would have to be met to identify a cell that drove specific turning behavior?
1) respond preferentially to rightward or leftward stimuli
2) have a contralateral partner with the opposite preference
btw they were found in small, ventral neurons in fish
where is swim speed encoded?
in firing rate of nMLF spinal projection neurons
dorsal neurons fire during fast swims
ventral neurons fire during slow swims
why are dorsal motor neurons less excitable ?
due to lower input resistance
they have lower input resistance.
higher input resistance ventral neurons turn on sooner
lesions of pyramidal tract selectively affect what?
dextrous movements
motor cortex is required for what?
learning new movements, but not reproducing them
